1. Field of the Invention
The present invention relates to a power tool having a housing, an electrical motor located in the housing and capable of rotation in both clockwise and counterclockwise directions, and having a commutator rotatable about an axis of the motor. The power tool further includes a brush carrier carrying at least two brushes that electrically contacts the commutator of the motor and an actuation member accessible from outside of the housing for rotating the brush carrier relative to the housing in a circumferential direction of the commutator between clockwise rotational position and counterclockwise rotational positions. The power tool also includes a device for preloading the brush carrier in both clockwise and counterclockwise rotational positions.
2. Description of the Prior Art
In power tools with a rotatable brush carrier of the type described above, the rotational positions are set in such a way that an optimal commutation takes place. Upon rotation of the brush carrier between rotational positions, the polarity of the motor connections changes whereby the rotational direction of the power tool also changes.
German Publication DE 101 52 963 discloses an electrical tool in which a bi-stable spring member engages the brush carrier and biases the brush carrier, after the brush carrier passed on unstable intermediate position, in a circumferential direction to one of two rotational positions. The spring member is formed as a leg spring which is arranged between the brush carrier and the housing and has one of its leg engaging the housing and its other leg engaging the brush carrier. In the axial direction, the brush carrier is supported against the housing at both of its sides.
The known preloading device insures a stable retention of the brush carrier in both rotational positions. In this way, in both rotational positions, a reliable and optimal commutation is achieved. In addition, a comfortable switching from one rotational position to another rotational position is achieved.
A drawback of the known preloading device of a power tool consists in that an axial or normal backlash between the brush carrier and the housing, which is necessary for a rotatable support of the brush carrier, is determined by the housing. Therefore, the manufacturing tolerances during manufacturing of the housing, temperature-induced deformation of the housing, in particular resulting form heating of the tool during operation, lead to disturbances during switching between rotational positions and to an erroneous position of the brush carrier relative to the commutator.
An erroneous position of the brush carrier relative to the commutator can lead to a poor commutation which, in turn, can result in a poor performance of the power tool.
Accordingly, an object of the present invention is a power tool in which the foregoing drawbacks are eliminated.
Another object of the present invention is a power tool which, having a simplified construction, would insure a stable and precise positioning of the brush carrier.